The present invention generally relates to methods for obtaining an electrical property of a test sample. The present invention relates to the measurement of sheet resistance and probe current leakage on shallow implanted regions in a semiconductor surface, and more particularly to the accurate and non-destructive measurement of sheet resistance on ultra shallow junctions.
A method for accurately determining the sheet resistance and leakage current density of a shallow implant in a semiconductor surface includes making one or more four-point resistance measurements with an induced current below 100 μA on the semiconductor surface with a plurality of electrode spacing sets, at least one set having an average spacing below 100 μm. The sheet resistance and implant leakage current density are determined through fitting the measured data to theoretical data to within a predetermined error.
Alternatively, the sheet resistance and implant leakage may be determined through fitting the measured data to theoretical data so as to obtain a minimal error, e.g. minimizing the error using numerical or other methods.
Related methods and techniques may be found in patent publications such as U.S. Pat. No. 4,703,252, U.S. Pat. No. 6,842,029, U.S. Pat. No. 7,078,919 and WO 2005/022135. Reference is made to the above US patent publications, all of which are hereby incorporated in the present specification by reference in their entirety for all purposes.
A transistor in a semiconductor circuit consists of two implanted regions, called the source and drain, connected electrically by a channel under a gate electrode. The Source Drain Extension (SDE) is a shallow implant that interfaces the channel under the gate with the deep source and drain. As transistors are made smaller, the SDE must be made extremely shallow to create a high performance device, as SDE depth is a key factor in transistor performance, especially fast switching speeds and low power requirements. At the 100 nm device technology node, depths of 20-30 nm are required, and future technology will need even shallower junctions. The term Ultra-Shallow Junction (USJ) refers to this extremely thin SDE.
Historically, macroscopic four-point probes have been the accepted way to measure the active dose in implanted surfaces. A macroscopic four-point probe is typically a millimeter-sized device with four spring-loaded transition metal needles in a single row. When the needles press against a surface, a current driven through the outer two pins generates a detectable voltage across the inner pins. This four-point measurement technique has been the standard way to measure sheet resistance on semiconductors for many years. However, macroscopic four-point probes perform poorly on the advanced ultra-thin films of today, as the spring-loaded needles tend to create surface damage and film penetration. The macroscopic probes also require large homogenous areas for measurements without edge artifacts. These limitations are particularly problematic on ultra shallow junctions. Several new technologies have appeared to address the issues with the conventional probes. These include macroscopic probes with low contact force and capacitive non-contact probes. These probing technologies address the destructive nature of conventional probing but fail to address the dimensional aspect of measurements on ultra shallow junctions: Macroscopic probes will consistently report too low USJ sheet resistance values, especially on high resistance implants with high leakage. Larger probe spacing will lead to larger deviations. While soft-touch or non-contact versions of the macroscopic probes solve issues with punch-through and surface damage, they tend to be even larger than the conventional probes, and thus suffer even more from this length scale problem.